It is well known in the art to suspend the drive belt of a snowmobile below the body thereof for suspension movements.
These suspension systems are usually provided with a pair of side rails to guide the drive belt, a pair of suspension arms each having a proximate end pivotally mounted to the snowmobile and a distal end pivotally mounted to both side rails. The side rails, suspension arms and the snowmobile are so configured as to form a deformable parallelogram, thereby allowing suspension movements of the side rails with respect to the snowmobile between a fully extended and a fully retracted position. Shock absorbers and compression springs are also provided between the side rails and the snowmobile to bias the side rails towards their extended position.
Such conventional snowmobile suspension systems suffer from many drawbacks. A first drawback relates to the material used to make the side rails. Indeed, side rails are usually made of aluminum which yields relatively heavy and complicated to manufacture side rails. Furthermore, aluminum side rails have other drawbacks related to the nature of the material such as, for example, poor resistance toughness and low fatigue life.
A second drawback of the conventional snowmobile suspension systems is revealed when a force, overcoming the forces applied by the shock absorbers and the springs, causes the side rails to go from their fully extended position to their fully retracted position. When this is the case, the side rails will hit the underside of the snowmobile, which may damage the vehicle and/or endanger the driver.
To overcome this drawback, commercially available snowmobile suspension systems are provided with a piece of resilient material, for example, rubber, strategically positioned to intercept the side rails before they contact the underside of the snowmobile. The contact is therefore much less violent since the resilient material absorbs a portion of the energy of the impact. However, the contact between the side rails and the rubber piece still causes undesired sensations to the driver.
A third drawback is the lack of adjustability of the suspension characteristics or the complexity of adjustment of these characteristics. Indeed, conventionally, the pivotal attachments securing the distal end of the rear suspension arm to the side rails and the shock absorbers to the side rails are at predetermined fixed positions which results, for a given configuration, in predetermined suspension characteristics. This is a drawback since it removes the possibility for the driver to select different suspension characteristics for different type of rides.
To address this problem, many adjustable snowmobile suspension systems have been proposed. For example, U.S. Pat. No 5,692,579 issued on Dec. 2, 1997, naming Keith W. Peppel et al. as inventors and entitled "Adjustable Snowmobile Track Suspension" discloses a system provided with a rear suspension arm having a distal end which is so mounted to the side rails that limited longitudinal movements of the distal end may be achieved. The systems also include adjustable limits allowing the characteristics of the suspension to be adjusted by the user.
While Peppel's suspension is an improvement in terms of adjustability, it involves many mechanical elements to allow the longitudinal movements and to limit these movements. Furthermore, the user needs some tools to loose the fasteners, rotate the rectangular limits and to tighten the fasteners.